This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Current techniques of measuring renal blood flow and GFR are time consuming and troublesome. They require either injection of a radioactive material or infusion of a substance for several hours with multiple urine and blood sampling. As a result, these methods are currently out of favor to use in clinical practice and are only reserved for research purposes. On the other hand, ultrasonography is a noninvasive and widely available technology with many uses in the field of nephrology. Recently the use of microbubbles as contrast agents to enhance ultrasound images has become popular in different medical fields. This technique is currently being utilized in imaging of the myocardium and coronary arteries. A few studies have demonstrated comparable accuracy of contrast enhanced ultrasound (CEU) to other conventional methods in diagnosing renal artery stenosis. In this pilot study, we will compare the accuracy of CEU in assessing the changes in renal blood flow in response to a high protein diet to the standard method using PAH clearance in healthy individuals. We will also evaluate the utility of CEU in assessing the changes in regional renal blood flow to cortex and medulla.